1. Field of the Invention
The present invention falls within the technical field that relates to an ink composition which is suitable for inkjet recording.
2. Description of the Prior Art
Conventionally, ink containing a dye, a humectant and water has been well known as ink used for inkjet recording. However, in the case of forming an image with the ink on a recording medium, the water-resistivity of the image is a matter of concern, i.e., there is a problem such that the dye exudes into water when the image is exposed to water. Especially when an image is recorded on plain paper, the water-resistivity of the image is very poor. (The “plain paper” herein refers to paper which is one of various types of commercially-available paper, which is especially used for an electrophotographic copying machine, and which is produced without an intention to have an optimum structure, composition, properties, or the like, for inkjet recording.)
In Japanese Unexamined Patent Publication No. 10-212439, Japanese Unexamined Patent Publication No. 11-293167, Japanese Unexamined Patent Publication No. 11-315231, and Japanese Unexamined Patent Publication No. 2000-178494, adding a hydrolyzable silane compound (organic silicon compound) to ink in order to improve the water-resistivity of an image formed with the ink on a recording medium has been proposed. When a drop of such ink containing a silane compound is adhered on a recording medium, and a water content (solvent) of the ink drop evaporates or permeates into the recording medium, the silane compound remaining on the recording medium is condensation-polymerized, and this condensation-polymerized silane compound encloses a dye. As a result, even when the image formed on the recording medium is exposed to water, the dye is prevented from exuding into the water.
However, it was found that an actual image recorded on a recording medium with any of the ink compositions proposed in the above conventional examples did not necessarily exhibit sufficient water-resistivity. That is, when the recorded image is soaked in water, the dye is dissolved in water or a bleeding occurs in the image because of water in some cases.
Furthermore, it was found that in the ink compositions containing some types of colorants, an effect of an aminosilane compound was not obtained, and therefore, the water-resistivity was hardly obtained. This is especially the case when a magenta dye is contained in the ink composition.